Thermoelectric conversion power generation is electric power generation by converting thermal energy into electric energy by using a phenomenon in which a voltage (thermoelectromotive force) is generated when a temperature difference is provided in a thermoelectric material, i.e., the Seebeck effect. Since the thermoelectric conversion power generation is capable of utilizing various waste heats such as geothermal heat, heat from an incinerator, and the like as heat sources, it is expected to be the electric power generation which is commercially practical and environment-friendly.
Energy conversion efficiency of the thermoelectric material is dependant on figure of merit (Z) of the thermoelectric material. The figure of merit (Z) is a value determined using Seebeck coefficient (α), electric conductivity (σ), and thermal conductivity (κ) by Equation (1):Z=α2×σ/κ  (1)and, as the figure of merit of the thermoelectric material is higher, a thermoelectric converter obtained therefrom has higher energy conversion efficiency. In particular, α2×σ in Equation (1) is called output factor and, as the thermoelectric material has higher output factor, the thermoelectric converter obtained therefrom has higher output per unit temperature.
The thermoelectric material includes a p-type thermoelectric material having positive Seebeck coefficient, and an n-type thermoelectric material having negative Seebeck coefficient. Typically, the thermoelectric converter in which the p-type thermoelectric material and the n-type thermoelectric material are electrically connected in series is used in the thermoelectric conversion power generation. Thus, the energy conversion efficiency of the thermoelectric converter is dependent on the figure of merit of each of the p-type thermoelectric material and the n-type thermoelectric material. In order to obtain the thermoelectric converter having excellent energy conversion efficiency, the p-type thermoelectric material and the n-type thermoelectric material each having high figure of merit are required.
As the n-type thermoelectric material, there is known a thermoelectric material obtained by mixing, molding, and sintering titanium oxide and tantalum oxide (or titanium oxide and niobium oxide) in air (JP-A-2005-276959).
However, the n-type thermoelectric material disclosed in the publication does not have sufficient output factor.